Conventionally, a semiconductor wafer made of silicon, gallium, arsenic or the like is produced in a state having a large diameter, then cut and separated (diced) into small element pieces, and further transferred to a mounting step. In this case, the semiconductor wafer is subjected to respective steps of a dicing step, a washing step, an expanding step, a pickup step and a mounting step in a state where the semiconductor wafer is stuck onto the pressure-sensitive adhesive sheet and retained thereby. As the above-mentioned pressure-sensitive adhesive sheet, there has been generally used a sheet in which an acrylic adhesive of about 1 to 200 μm in thickness is applied onto a base material composed of a plastic film.
The above-mentioned dicing step is usually performed using a round blade (dicing blade) which moves with rotating. In that case, cutting with the round blade is performed so that the blade reaches an inside of the base material of the pressure-sensitive adhesive sheet for dicing which retains the semiconductor package. At this time, when cutting is performed into the inside of the base material of the pressure-sensitive adhesive sheet, the plastic film itself as the base material generates fibrous scraps thereof. When the fibrous scraps are adhered to a side of a semiconductor chip, the semiconductor chip is mounted in a state where the fibrous scraps are adhered. As a result, the fibrous scraps have caused a problem of a significant reduction in quality of an electronic circuit.
As a means for solving such a problem, for example, JP-A-5-156214 (patent document 1) proposes a wafer sticking sheet using an ethylene-methacrylate copolymer as a base material. However, although this wafer sticking sheet inhibits the generation of fibrous scraps in some degree, it does not satisfy a level which is endurable in the dicing step performed for obtaining further highly reliable semiconductor devices.
Further, JP-A-5-211234 (patent document 2) discloses a pressure-sensitive adhesive sheet for wafer sticking using a polyolefinic film irradiated with an electron ray or a γ-ray at 1 to 80 MRad as a base material film. However, in this pressure-sensitive adhesive sheet for wafer sticking, the damage of the base material film caused by the radiation is extensive, and it is difficult to obtain a film excellent in appearance. Moreover, a great deal of cost is required in the production of the base material film.
Furthermore, JP-A-2003-257893 (patent document 3) discloses a pressure-sensitive adhesive sheet for dicing using a base material film which contains an olefinic thermoplastic elastomer containing propylene and ethylene and/or an α-olefin having 4 to 8 carbon atoms as polymerization components and having a melting point peak temperature of 120° C. to 170° C., and an ethylenic polymer containing ethylene as a main polymerization component. However, this pressure-sensitive adhesive sheet for dicing has the trade-off relation that the occurrence of whiskers can be reduced by an increase in the ratio of propylene contained in the base material film, whereas expandability is deteriorated. Namely, the above-mentioned constitution can inhibit the occurrence of fibrous scraps, but it is necessary to sacrifice expandability to some degree.
Furthermore, as a means for solving the problem of expandability, for example, JP-A-2-215528 (patent document 4) discloses a multilayer film for dicing in which a thermoplastic resin having rubber elasticity and an ethylenic resin layer are laminated with each other through a pressure-sensitive adhesive layer or directly. Further, it is described that the thermoplastic resin having rubber elasticity is a polybutene-1, polyurethane or polyester elastomer, or a saturated thermoplastic elastomer having a crystallinity of 5% to 50% and an average molecular weight of 80,000 or more, which is obtained by hydrogenating a 1,2-polybutadiene, styrene-butadiene-styrene or styrene-isoprene-styrene block copolymer. However, although this multilayer film for dicing improves expandability, a lot of fibrous scraps are generated in dicing. Accordingly, it is difficult to produce a semiconductor chip which secures high reliability.
Patent Document 1: JP-A-5-156214
Patent Document 2: JP-A-5-211234
Patent Document 3: JP-A-2003-257893
Patent Document 4: JP-A-2-215528